Alien atmosphere helped unfreeze ancient Earth

Published: Wednesday, January 14, 2009, 12:19 [IST]

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Washington, Jan 14 (ANI): Analysis of the chemical composition of 635-million-year-old rocks from the Norwegian island chain of Svalbard has revealed oxygen trapped inside the rocks, which suggests ancient Earth once had an alien atmosphere that might have helped melt millions of years' worth of deep freeze.

According to a report in National Geographic News, the analysis shows a surprisingly low amount of a particular type, or isotope, of oxygen.

Reduced levels of this isotope are linked to high levels of carbon dioxide in the atmosphere, and the new data suggest ancient Earth might have had 300 to 1,000 times more CO2 than current levels.

An atmosphere so rich in CO2 would still be breathable by modern standards, but it would place limits on the growth of life as we know it.

"The numbers indicate a very, very different world" than scientists had previously assumed, said study leader Huiming Bao of Louisiana State University.

Bao and colleagues think their finding supports the "snowball Earth" theory, which says that snow and ice accumulation worldwide once reached a threshold that caused the entire planet to stay frozen for millions of years.

Most scientists believe Earth could only emerge from such a state after ten million years or more, after atmospheric CO2 built up enough to finally trigger melting and lead to a rapid thaw.

Bao and colleagues analyzed a compound called sulfate from rocks dated to the Neoproterozoic era, which lasted from a billion to 542 million years ago.

Sulfate forms when a charged sulfur atom binds with four oxygen atoms. The complete molecule is highly stable, which makes sulfate a useful tool for studying what types of oxygen atoms were present when the sulfate formed.

In the Svalbard study, Bao and colleagues looked at the sulfate-containing mineral carbonate and found very low levels of an oxygen isotope called O-17.

Previously, Bao and a different set of co-authors had examined sulfate in another mineral called barite in samples from south China and West Africa dated to roughly the same time period.

Those rocks had also shown a low amount of O-17.

Given that the abnormal isotope ratios occurred in several locales, University of California, San Diego, chemist Mark Thiemens beleives the results are associated with a widespread phenomenon.

The atmospheric effects were, "if not global, at least equatorial," said Thiemens.

According to geophysicist Raymond Pierrehumbert, of the University of Chicago, the result "underscores what I call 'Neoproterozoic weirdness,' namely that there are a lot of strange geochemical signatures that indicate that the climate is doing something radically different from what it was doing before or since." (ANI)